Beginning in 230 BC, the Qin under King Ying Zheng engaged in a series of wars conquering each of the rival states that had previously pledged fealty to the Zhou.

They sought to create a strong, centralised state and a large army supported by a stable economy, which were developed in the Qin homeland and implemented across China following its unification.

Reforms included the standardisation of currency, weights, measures, and the writing system, along with innovations in weaponry, transportation and military tactics.

The central government sought to undercut aristocrats and landowners and administer the peasantry directly, who comprised the vast majority of the population.

This enabled numerous large-scale construction projects involving the labour of hundreds of thousands of peasants and convicts – which included the connection of walls along the northern border into what would eventually become the Great Wall of China, a large national road system, and the city-sized Mausoleum of Qin Shi Huang guarded by the life-sized Terracotta Army.

The state possessed an unprecedented capacity to transform the environment through the management of people and land; as a result, Qin's rise has been characterised as one of the most important events in East Asian environmental history.

When Qin Shi Huang died in 210 BC, two of his advisors placed an heir on the throne in an attempt to exert control over the dynasty and wield state power.

[7] The state of Qin began military expeditions into central China in 672 BC, though it did not engage in any serious incursions due to the threat from neighbouring tribesmen.

From the preceding Spring and Autumn period (c. 770 – c. 481 BC), the prevailing philosophy had dictated war as a gentleman's activity; military commanders were instructed to respect what they perceived to be Heaven's laws in battle.

Unlike many of their enemies, the Qin utilised contemporary advancements in weapons technology and transportation, the latter of which enabled greater mobility across the different types of terrain throughout China.

[13] The geography of Qin's core territories – located at the heart of a region known as the Guanzhong – provided additional advantages, including fertile farmland, and a strategic position protected by mountains that made it a natural stronghold.

"[5] The Qin's agricultural output, expanded via projects like the Wei River canal built in 246 BC, helped sustain their large army.

The Qin army was unfamiliar with the jungle terrain, and it was defeated by the southern tribes' guerrilla warfare tactics with over 100,000 men lost.

As expected, Qin Er Shi proved inept: he executed many ministers and imperial princes, continued massive building projects – one of the most extravagant was the lacquering of the city's walls – enlarged the army, increased taxes, and arrested messengers who delivered bad news.

The emperor's quarters were invaded, and Qin Er Shi was forced to commit suicide for his incompetence after being cornered by Zhao's co-conspirator and son-in-law Yan Le [zh].

[26] Unrest continued to spread among the people – caused in large part by regional differences, which had persisted despite Qin's attempts to impose uniformity – and many local officials had declared themselves kings.

[28][note 3] With the former Qin territories temporarily divided into the Eighteen Kingdoms,[30] Liu Bang then betrayed Xiang Yu, beginning the Chu–Han Contention from which he ultimately emerged victorious atop a reunited realm – on 28 February 202 BC, he declared himself emperor of the newly founded Han dynasty.

[23] The Qin aristocracy were largely similar to the Zhou in culture and daily life, with regional variation generally considered a symbol of the lower classes – and ultimately as contrary to the unification that the government strove to achieve.

[36] The dominant religious belief in China during the Qin, as well as throughout the early imperial period, was focused on the shen (roughly meaning 'spirits'), yin ('shadows'), and the realm they were understood to inhabit.

Zheng and his advisors also introduced new laws and practices that ended aristocratic rule in China, fully replacing it with a centralised, bureaucratic government.

[46] Unlike the Han, who initially continued the use of banliang, the Qin did not allow additional coins to be minted by the private sector, and considered those that were to be counterfeit.

生者著，死者削 Those who are born shall be entered, and those who die, expunged During the 4th century BC, the state of Qin introduced a registration system for its population, which initially collated the names of individuals, and later began keeping track of entire households.

Writing was adopted throughout the Zhou cultural sphere during the first half of the 1st millennium BC, with the shapes and forms of characters in the script gradually evolving over time.

[56] While the regional divergences across China were reduced considerably, the use of variant characters remained frequent among Qin scribes; the traditional idea of a strict standardisation of small seal script appears to be a later notion introduced by the Han.

[61] Comparative model manuals guided penal legal procedures based on real-life situations, with publicly named wrongs linked to punishments.

Li Kui's Canon of Laws – a lost text which Shang Yang was said to have been drawn from, a claim supported by other Qin-era manuscripts – treated dealing with thieves and robbers as the most urgent legal matter of its time.

[65][66] Depicted as emphasising law and order, Sima Qian also relates Qin Shi Huang as praising himself as being a "sage ruler of benevolence and righteousness ... who cares for and pities the common people".

Criminals were sometimes given amnesties, only incurring punishment upon recidivism, and were often pardoned in exchange for fines, labour, or a demotion in aristocratic rank, even for capital offences.

While The Book of Lord Shang recommended harsh punishments, it also "laments" insufficient population for its territories, and the Qin attempted to limit emigration out of the country.

[73] During the 2nd and 1st centuries BC, Han dynasty scholars began portraying the Qin as a monolithic, legalist tyranny, often invoked as an example of bad governance in contemporary debates about imperial policy.